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[Reprinted from the Yearbook of the U. S. Department of Agriculture for 1895.] 

REASONS FOR CULTIVATING THE SOIL. 

By Milton Whitney, 
Chief of the Division of Agricultural Soils, U. S. Department of Agriculture. 

HOW WATER ENTERS THE SOIL. 

Water is the most abundant substance found in living crops. Not 
only does it form by far the largest proportion of all fresh vegetable 
substance, but, on account of loss through evaporation from the leaves 
of growing plants and the necessity of replacing this loss, thirty or 
forty times more water is needed during the growing period of a crop 
than is contained in the crop when harvested. Plants require a large 
amount of water for their life and growth, and it is necessary that the 
supply should be abundant at all times. If the evaporation from the 
plant greatly exceeds the amount taken" in through the roots, the 
leaves wilt and the plant suffers. ^ 

Therefore one of the most important functions of the soil in its 
relation to crop production is the maintenance of a proper supply of 
water. Rain falls, on an average, in the humid portion of the United 
States for two or three days in succession, and is then followed by 
an interval of eight or ten days of fair weather. As plants are fixed 
in their relative positions in the earth, the soil, in order to supply 
them with water during the fair-weather period, has to offer such a 
resistance to the percolation of the rain that an adequate supply shall 
be held back. On account of this resistance, due to the friction which 
the rain encounters in the minute spaces between the soil grains 
through which it has to pass, the movement is very slow and only 
part of the water sinks below the reach of plants before the next 
rainfall occurs. 

The resistance which soils, owing to their difference in texture, 
offer to the percolation of the rain varies greatly. Light, sand}^ soils 
maintain comparatively little moisture, because the spaces between 
the grains are- comparatively large and there is relatively iDut little 
resistance to the flow of water, so that the rainfall moves down quite 
rapidly until there is only 5 or 10 per cent of moisture present in the 
soil. Strong clay soils, on the other hand, have very minute spaces 
for the water to move through, and consequently offer a very great 

' This subject was treated quite fully in an article by G-alloway and Woods on 
" Water as a factor in the growth of plants," in the Yearbook for 1894. 

123 



124 YEARliOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

resistance to tlie percolation of the rain. These soils maintain, as a 
rule, from 15 to 20 per cent of their weight of water. 

Different plants grow best with diflferent amounts of water. For 
instance, the pasture grasses thrive on a soil which is too moist for 
Indian corn, or even for the largest and surest yield of wheat. Some 
classes of tobacco thrive well on soils which are very retentive of mois- 
tiire, while other classes can only be grown with success on drier soils. 
We ai-e not concerned in this article with tlie amount of moisture 
which different soils maintain or with the amount of moisture required 
by different kinds of plants. We must recognize, however, that it is 
not p(>ssil)le nor desirable to maintain the same amount of water in 
all soils, for if this were done there would not be the opportunity for 
diversity in agriculture which we have under existing conditions. 

While water is maintained for a time in the soil, as already explained, 
it is liable to be lost to the growing crop by evaporation from the sur- 
face of the ground or by being used up by weeds. The end sought 
in plowing and cultivation is to control the water supply by removing 
weeds and leaving the surface of the soil covered with a loose, drj^ 
mulch to retard evaporation. Many of our crops require no subse- 
quent cultivation after they are put into the ground. Wheat, oats, 
rye, clover, grass, forest trees, and, in general, such crops as cover and 
shade the ground are not, as a rule, cultivated during their period of 
growth. On the other hand, such crops as corn, tobacco, cotton, pota- 
toes, and fruit trees require cultivation during theii' early growing 
period, although even with these crops cultivation ceases after they 
have attained considerable size, and is rarely practiced during the 
ripening period. 

The principal object of plowing is to loosen up the soil, for four 
purposes: (1) To enable the soil to absorb the rainfall more quicklj^ 
and more freely than it would in its undisturbed condition; (2) to 
maintain more of the rainfall near the roots of ijlants; (3) to admit 
fresh air to the roots of plants; (4) to enable the roots of the young 
oi' (luickly growing plants to penetrate the soil more easily. 

The principal objects of subsequent cultivation, whether with plow, 
cultivator, cotton sweep, harrow, hoe, or rake, are (1) to prevent loss 
of water by weeds and grass, which use up great quantities; (2) to 
keep the surface covered with a loose, dry mulch in order to prevent, 
so fai- as possible, loss of water by evaporation. Water is thus con- 
serN'ed for the use of crops, and the supi3ly is more abundant and 
more uniform than it would have been without the cultivation. 

A soil with a compact surface quickly dries out, and the water 
supply fi actuates rapidly and excessively, to the detriment of most 
cr(jps dui-iug their growing period. Weeds and grass are generally 
to be excluded from the crop because tliey transpire great quantities 
of water which would othermse have been at the disposal of the crop. 
Weeds ai-e, however, occasionally of advantage to the crop, especially 
during 1h(^ i'ii)ening period, because they help to dry out the soil and 
thus hasten the maturity of the crop. 



REASONS FOR CULTIVATING THE SOIL. 125 

Some of our crops, therefore, do not require cultivation, because 
they shade the ground and prevent evaporation and prevent grass 
and weeds from springing up and diminishing their supply of water, 
or because they are deeply rooted and can bring water up from con- 
siderable depths. Other crops can not protect their water supply 
in this way, and it must be artificially controlled by methods of 
cultivation. 

In tropical countries where rain falls nearly every day, giving an 
abundant and uniform supply of moisture in the soil, crops require 
little or no cultivation, and only the larger weeds need be removed 
from the field. The rainfall is sufficient, both in amount and distri- 
bution, for the support of the weeds and an average crop. 

PRINCIPLES OF PLOWING. 

The common plow is essentially a wedge-shaped instrument, which 
is forced through the soil to loosen it. The topsoil is forced aside, 
thrown up, and usually turned over. This action loosens the soil by 
separating the soil grains. The loose soil occupies more space than the 
compact soil did, and a cubic foot of the former, therefore, contains 
more space for water to enter. Each separate space, however, is also 
larger and has less capillary action and a smaller power of drawing- 
water to the surface. If the soil, by reason of its fine texture or wet 
condition, is lumpy after the plowing, the spaces in the soil will be of 
very uneven size, and it frequently happens that the surface of the 
ground is not left in a suitable condition to draw water up from below. 
If small seeds are sown on such a rough surface, they are liable to 
suffer for lack of moisture. It is customary, therefore, and very advis- 
able in such cases, to harrow and roll the seed bed until all the larger 
lumps are broken down and the surface is left smooth and even, in 
order to insure a supply of moisture to the seed during the germinating 
period. However, soil which has thus been rolled will lose more water 
b}' evaporation than soil which has been simply harrowed. The evapo- 
ration of this moisture is an incident which it is not always possible 
or desirable to prevent. With some crops the surface may be har- 
rowed after the seed has germinated. This is desirable when it can be 
done without injury to the crop, as it tends to retard evaporation. 

There is one serious defect in the principle of the common plow 
which, upon some soils and with certain kinds of plowing, is liable to 
have very serious effects. If a field is plowed for many successive 
years to a depth of 6 or 8 inches the tendency each time is to com- 
pact the subsoil immediately below the plow, thus rendering it more 
impervious to water; that is, the plow in being dragged along plasters 
the subsoil just as a mason with his trowel would smooth out a layer 
of cement to make it as close and impervious to water as possible. 
This is undoubtedly an advantage to some soils, but, on the other 
hand, it is very injurious to many. 

The injurious effect of this compact layer formed by the plowing is 
twofold. It makes it more difficult for the rainfall to be absorbed as 



126 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

rapidly as it falls, and increases the danger of loss of water and injury 
to the soil by surface washing. Soils plowed at a depth of 3 or 4 
inches, which is quite common in many parts of the country, would 
have a thin layer of loose material on the surface, with a compact 
subsoil below, into which water would descend rather slowly. With 
a rapid and excessive fall of rain, the light, loose topsoil is liable to 
be washed away by the excess of water, which can not descend into 
the subsoil as rapidly as it falls. This washing of the surface and 
erosion of fields into gullies occasion the abandonment of thousands 
of acres of land. The field will not wash so badly if it is not plowed, 
and, on the other hand, it will hardly wash at all if the cultivation is 
deeper and the subsoil left in a loose and absorbent condition. The 
deeper the cultivation, the greater the proportion of rainfall stored 
away and the less danger of the erosion of the surface soil and the 
less serious the defect of our common method of plowing. While 
there is less danger from washing, however, with deep cultivation, 
there is still a tendency toward the formation of a hardpan at what- 
ever depth the land is plowed. No simple modification of the ordi- 
nary plow or of the subsoil plow will overcome this defect. It will 
require a change in the very principle of the implement. The plow 
should not cut through the soil, but break it ai)art so as neither to 
compact nor puddle it by being dragged along over the subsoil. 

While all other farm implements and machinery have been im- 
proved, especiall)^ Avithin the last fifty years, so that we are able 
now to harvest more crops than ever before and to handle our 
crops to better advantage, our common plow has not been essen- 
tially iniproved or modified in any important particular, except as 
to mechanical construction, since the days of the early Greeks and 
Romans. It would seem only necessary to call attention to this, the 
fundamental and simplest principle of agriculture, to have some new 
method devised of stirring the soil without compacting the subsoil. 

The highest art of cultivation which has ever been practiced is 
that of trenching, so extensively employed in England and so ear- 
nestly advocated I)}' the early English writers on agriculture. With a 
large class of lands there is no implement so effective for loosening 
and improving the soil conditions as the spade. The spade does not 
cut the soil from the subsoil as the plow does, but breaks it off, and 
there is little or no disturbance and no compacting whatever below 
that point. Everyone is familiar with the difference in the tilth of 
a garden which has been thoroughly spaded and of a field plowed 
in the oi-dinary way. This old method of trenching Avith a spade 
can not, of course, be used in the extensive systems of cultivation 
practiced in this country, and it is now used in England much less 
than it was years ago, but if this principle could be worked into a 
pi-aci ical method of cultivation it would be of great benefit to agri- 
culture. 



REASONS FOR CULTIVATING THE SOIL. 127 

PRINCIPLES OF SUBSOILING. 

At the present time little is known definitely about the practical 
value of subsoiling. In certain localities it has or has not been 
found to be beneficial to crops. There is a wide difference of opinion 
upon this fundamental, point. Fifteen or twenty years ago it was 
very generally advocated throughout the East by all of the agricul- 
tural journals. It was tried in a great variety of soils and under 
many conditions, and there is no doubt that in perhaps a majority 
of cases it showed no beneficial effects. This might have been 
expected, for no one method of cultivation can be equally valuable 
under the various conditions of soils, climate, and crops such as 
prevail over such a great extent of country. At present the subject 
is being prominently agitated in some of the Western States, particu- 
larly in the semiarid regions, and very favorable results are being 
reported through the local agricultural papers. 

A few general principles only may be laid down for guidance in 
this matter. Subsoiling is rarely necessary in light, porous, sandy 
soils or in a climate where there are frequent light showers. It is not 
beneficial in heavy, wet soils, unless they are previously thoroughly 
underdrained. It is likely to be injurious if in the operation much 
of the subsoil is brought to the surface and incorporated in the sur- 
face soil, especially if the subsoil itself is in an unhealthy condition 
as regards drainage and contains poisonous matters which would be 
deleterious to plant growth. Poisonous matters frequently occur in 
subsoils as a result of improper aeration and the growth of certain 
minute organisms. 

Subsoiling when properly done consists merely of breaking up the 
subsoil without bringing it to the surface or in any way incorporating 
it with the upper layer of the soil. In this respect it differs from 
deep plowing. The ideal subsoil plow consists merely of a tongue 
fashioned much like a common pick and hardly larger in its dimen- 
sions — slightly smaller at the point than in the rear, but as small in 
all its parts as is consistent with perfect rigidity and with the nature 
of the soil through which it is to be drawn. This usually follows an 
ordinary plow. It should be run at as great a depth as possible, the 
endeavor being to get it at least 16 or 18 inches below the surface. It 
is often advisable by this means to break up a hardpan formed, per- 
haps, by long-continued plowing at a uniform depth or existing as a 
natural formation below the surface. 

Subsoiling is likely to be beneficial, under the prevailing climatic 
conditions east of the Mississippi River, in any soils of medium or of 
heavy texture,, provided the land has fairly good drainage. In the 
semiarid region of the West it is likely to be very beneficial upon 
many classes of soils, especially where the rainfall occurs in heavj^ 
and infrequent showers and where it is necessary to increase the 
capacity of the soils to absorb water readily and rapidly. 



128 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

Subsoiliiig, to be efficient, should be done a sufficient length of time 
before the crops are jjlanted to insure to the soil a thorough soaking 
with rain; otherwise it may injure rather than improve the soil con- 
ditions for the first year. Subsoiling by stirring the land to an 
unusual depth favors tlie drjing out of the soil, so that if it is not 
supplemented by a soaking rain before the seed is put in, the ground 
is drier than if the work had not been done. This fact has been 
shown to a notable extent in central and western Kansas during the 
present season and has been commented upon in Bulletins Nos. 1, 2, 
and 3 of this division. 

There are few places in the West where this practice has been carried 
on long enough and under conditions necessary for beneficial effect. 
One such place, however, is at Geneva, Nebr. , where subsoiling has 
been intelligently carried on for a number of years under nursery 
stock. The records of soil moisture which have been made at that 
place by this division through the present season show that on the 
average, through the months of June, July, and August, there was 10 
lier cent of moisture in the soil to a depth of 12 inches where ordinary 
methods of cultivation had been used, and 15 per cent where the land 
had lieen previously subsoiled. No crops were growing on the soils 
from which the records were kept in either case. This difference of 
5 per cent in the amount of water, or 50 i^er cent increase over that 
in the uncultivated soil, is a very large amount and would doubtless 
have a very important effect upon the crop yield. This is confirmed 
by the actual yields on the two soils, as reported by Younger & Co. , 
on whose farm the observations were made. 

Further work will be done along these lines by this division, to 
establish these general principles. In the meantime great care and 
judgment should be exercised in deciding upon whether it is advisable 
to adopt this practice in every case. 

CULTIVATION. 

Cultivation as here used means the actual stirring of the surface 
after the croj) is planted, either with a plow, cotton sweep, cultivator, 
hari'ow, hoe, or other implement. The object of cultivation is two- 
fold — to destroy weeds and thus prevent the great drain which they 
make upon the soil moisture, and to loosen and pulverize the surface, 
leaving it as a fine mulch, the object of which is to prevent evapora- 
tion. The first of these objects needs no further comment here. As 
regai'ds the second ol)ject of cultivation, the result to be attained is 
to have the surface covered with a fine, dry mulch before the dry sjiell 
sets in, so as to conserve the water in the soil during dry periods. 

Cultivation is usually most effective in the early stages of the 
growth of crops, especially during the growth of the vegetative parts 
of the plant . It is usual to stir the surface after each rain. If another 
rain follows within a short time, this cultivation may do little or no 
good; but if a dry season follows, the cultivation may save the crop 
by its having diminished the evaporation. While cultivation does 



REASONS FOR CULTIVATING THE SOIL. 129 

not add water to the soil, as some claim, it prevents excessive loss, and 
thus maintains more water in the soil, which means about the same 
thing. 

The kind of treatment adapted to the cultivation of different soils 
depends upon local conditions, climate, and the kind of crop. The 
object sought is the same in all cases, but the means of attaining it 
must be adapted to the local circumstances. As a rule, cultivation 
should be shallow, for two reasons, namely, to avoid disturbing the 
roots of the growing plants, and to avoid losing any more of the soil 
moisture than possible. A single cultivation after each rain is not 
necessarily enough, especially if a dry season is expected. The sur- 
face must be kept loose and dry, and this may require more than one 
cultivation, even if there has been no subsequent rain. 

Few of our agricultural crops require cultivation after they have 
attained their vegetative growth, and a crop is frequently injured 
when cultivation is continued too long, because the soil is thus kept 
too wet, and the plants are not inclined to ripen as early as they 
should or to mature as large a jield of fruit or grain. Most of our 
grain crops will mature more seed if the ground is moderately dry 
during their ripening period. 

UNDERDRAINAGE. 

A soil containing too much water during the whole or a considerable 
part of the season should be underdrained to draw off the excessive 
amount of moisture. Most of our agricultural crops do better in a 
soil containing from 30 to 60 per cent of the amount of water which 
the soil would contain if saturated. With less water, crops suffer; 
with more, they suffer from lack of air around their roots. Wheat 
may be grown very successfully, and will attain a perfectly normal 
development in water culture with its roots entirely immersed in a 
nutritive solution, provided the water is supplied with air at frequent 
intervals, but it will not grow in a stagnant, saturated soil, not because 
there is too much water, but because there is too little air. A soil, 
therefore, which contains too much water contains too little air, and 
part of the water should be drawn off through ditches or tile drains. 

Centuries ago the Romans used to overcome this trouble by plant- 
ing the crop on very high ridges or beds, often 8 or 10 feet high and 
fully as wide. In this way alleys were provided at frequent intervals 
to carry off the surface water, and the greatest extent of surface was 
presented for the drying out of the soil, while the roots were kept at 
a considerable distance from the saturated subsoil. Storer states 
that some of these ridges are still to be found in localities in Europe. 
They are used to-day in a modified form in the cultivation of the sea- 
island cotton off the coast of South Carolina, but are being gradually 
given up as the practice of underdrainage is introduced, which is 
cheaper in the end and more effective. 

Tile drainage is usually most effective in stiff clay soils and in low 
bottom lands, but it is occasionally beneficial in medium grades of 



130 YEARBOOK OF THE U. S. DEPARTMENT OF AGRICULTURE. 

loam or even in light sandy soils. It is practiced to a considerable 
extent in the light sandy soil of the truck area of the Atlantic Sea- 
board, where the question of a few days in the time of ripening of the 
crop is an important factor. 

IRRIGATION. 

If the climatic conditions are such that it is impossible, with the 
most improved methods of plowing, subsoiling, and subsequent culti- 
vation, to maintain a sufficient amount of moisture in the soil for the 
use of crops, it is then necessary to resort to irrigation or the artifi- 
cial application of water to the soil. It is not the purpose here to 
enter into a discussion of the best methods of irrigation, but simply 
to discuss briefly the general principles of irrigation as practiced in 
maintaining jjroper conditions in the soil. 

Our ideas of irrigation should not be confined to the arid regions. 
To be sure, irrigation is much more important there than elsewhere, 
for without artificial application of water crops could not be produced 
in many localities. In the humid i)ortion of the United States, even 
in localities in Florida where they have from 60 to 70 inches of annual 
rainfall, irrigation is used successfully as a means of insuring the 
crop against drought due to the uneven distribution of the rainfall. 
It has been pointed out in several publications of this division that 
where the supjDly of water in different soils reaches a certain point, 
which differs according to the texture of the soil, crops suffer for lack 
of it. In the truck soils of the Atlantic Coast this minimum is ap- 
proximately 4 per cent, while in the heavy limestone grass lands of 
Kentucky the pasture begins to dry up when the soils contain as much 
as 15 per cent of water. 

Under our present modes of cultivation the farmer can do little for 
the crop during the time of actual drought. Ordinary cultivation is of 
comijaratively little benefit during a prolonged dry season. Its most 
elfective work is before the dry spell sets in. No matter what the 
value of the crop, and no matter how much this value is concentrated 
on small areas of land, tlaiere is practically but little to be done to 
save the crop. Irrigation should be used as an insurance against the 
loss of crops. A small pond fed by a windmill would often save a 
garden or a small area of a valuable croj) from destruction or great 
injury during a dry season. A small portable farm engine, which 
would be available at other times for cutting feed, thrashing grain, 
and other farm jjurposes, could be used to drive an irrigating pump, 
during the dry seasons. This would be particularly valuable for 
tobacco, truck, and other crops which are grown under a very inten- 
sive system of cultivation. 

The object of all cultivation, in its broadest aspect, is to maintain, 
under existing climatic conditions, a uniform and adequate supply of 
water and air in soils adapted to different classes of plants. This is 
the object alike of plowing, subsoiling, cultivation, underdrainage, 
and irrigation ; they are all processes to be used in maintaining 
suitable moisture conditions for the growth of crops. 



